1. Field of the Invention
The present invention relates to a solid-state imaging device of single-chip type, for use in a color video camera or the like, and more particularly to a method of driving the solid-state imaging device.
2. Description of the Related Art
As is known in the art, a solid-state imaging device of single-chip type is used in great numbers, in which imaging elements are driven by so-called "field integration method." In the field integration method, adding two signals representing two adjacent pixels of the same column, in one way during the period of every odd-numbered field, and in another way during the period of every even-numbered field. In other words, the "field integration method" performs interlacing. With color filter array shown in FIG. 1, so-called "line sequencial color difference signal method", during each field period, a line signal consisting of color pixel signals G+C and M+Y alternately recurring, and a line signal consisting of color pixel signals M+C and G+Y alternately recurring are alternately output by the solid-state imaging device. The four signals G+C, M+Y, M+C, and G+Y are defined as follows: EQU G+C=2G+B EQU M+Y=2R+G+B EQU M+C=R+G+2B EQU G+Y+R+2G
where G is green, C is cyan, B is blue, M is magenta, Y is yellow, and R is red. A signal-processing circuit (not shown) combines these color signals, thereby generating signals representing three primary colors, i.e., red, green, and blue.
The line sequential color difference signal mehod is advantageous in that data of all pixels is read out within one-field period, enhancing the time-domain resolution without reducing the sensitivity of the imaging device. The method is disadvantageous in the following respect, however. Two signals representing two adjacent pixels of a column are added, generating a signal for one row. Further, two adjacent signals representing two other adjacent pixels of the same column are added, thus generating a signal for the next row. Next, the correlation between the two adjacent rows of pixels is determined, thereby generating a color signal. After all, to obtain one color signal, four signals representing four adjacent pixels of the same column must be processed. Consequently, the solid-state imaging device can generate signals, but those representing an image having an insufficient vertical resolution.
A solid-state imaging device has been developed, which can generate signals representing images having sufficient resolution, without impairing the above-mentioned advantage inherent in the line sequential color difference signal method. This device, generally known as "two-line reading device," has the structure shown in FIG. 2A. More specifically, the device comprises photoelectric converting elements 11 charge-transferring stages 12, two horizontal charge transfer elements 13 and 14, two detectors 15 and 16, and two output terminals 17 and 18.
The photoelectric converting elements 11 are arranged in rows and columns. They are provided in numbers large enough to detect a full frame of an image. The charge-transferring stages 12 are provided in the same numbers as the photoelectric converting elements 11, associated with the photoelectric converting elements 11, respectively, and are arranged, forming columns which extend along the columns of elements 11, respectively. Each of the stages 12 transfers the electric charge of the associated photoelectric converting element 11 to the next stages 12 of the same column. Hence, each column of stages 12 transfers the charges accumulated in the elements 11 in the vertical direction.
The horizontal charge transfer registers 13 and 14 extend in the horizontal direction. The register 13 has a row of charge-transferring stages provided in the same number as the charge-transferring stages 12 of one row and associated with the columns of charge-transferring stages 12 of the respective columns. Each charge-transferring stage of the stage 13 receives an electric charge from the last stage 12 of the associated column. The register 14 has a row of charge-transferring stage provided in the same number as those of the charge transfer regtister 13 and associated with therewith, respectively. Each charge-transferring stage of the register 14 receives an electric charge from the charge-transferring stage of the register 13. Either charge transfer stage transfers the electric charges defining one line of an image frame in the horizontal direction.
The detector 15 detects the charges defining one line of the image frame, horizontally transferred in the transfer register 13 and successively output there from, and converts these charges into voltage signals. Similarly, the detector 16 detects the charges defining the preceding line of the image frame, horizontally transferred in the transfer register 14 and successively output therefrom, and converts the charges into voltage signals.
The output terminal 17 supplies the voltage signals output by the detector 15, to a signal-processing circuit (not shown). The output terminal 18 supplies the voltage signals output by the detector 16, to the signal-processing circuit.
During the period of each even-numbered field of a frame, the solid-state imaging device operates in the following way. First, as is shown in FIG. 2A, the photoelectric converting elements 11 accumulate the electric charges 1 to 7 defining the frame. As is evident from in FIG. 2B, these charges are simultaneously transferred from the elements 11 to the charge-transferring stages 12. Then, as is shown in FIG. 2C, the charges are transferred in the columns of the stages 12, in the vertical direction, whereby the charges defining one line of the frame are supplied to the horizontal transfer register 13. Next, as is shown in FIG. 2D, the charges are further transferred in the columns of the stages 12, in the vertical direction, whereby the charges defining the line of the frame are supplied to the horizontal transfer register 14, while the charges defining the next line of the frame are supplied to the horizontal transfer register 13. Then, the detector 16 converts the charges defining the second line of the frame into voltage signals. At the same time, the detector 15 detects converts charges defining the second line of the frame into voltage signals. Finally, the output terminals 17 and 18 supply the signals output by the detector 15 and those output by the detector 16 to the signal-processing circuit (not shown).
During the period of each odd-numbered field of a frame, the solid-state imaging device operates in the following way. First, as is shown in FIG. 3A, the photoelectric converting elements 11 accumulate the electric charges 1 to 7 defining the frame. As is evident from in FIG. 3B, these charges ar simultaneously transferred from the elements 11 to the charge-transferring stages 12, and are transferred in the columns of the stages 12, in the vertical direction, whereby the charges defining one line of the frame are supplied to the horizontal transfer register 13. Next, as is shown in FIG. 3C, the charges are further transferred in the columns of the stages 12, in the vertical direction, whereby the charges defining the line of the frame are supplied to the horizontal transfer register 14, while the charges defining the next line of the frame are supplied to the horizontal transfer register 13. Further, as is shown in FIG. 3D, the charges are further transferred in the columns of the stages 12, in the vertical direction, such that the charges defining the second line of the frame are supplied to the horizontal transfer register 14, while the charges defining the third line of the frame are supplied to the horizontal transfer register 13. Then, the detector 16 converts the charges defining the third line of the frame into voltage signals. At the same time, the detector 15 detects converts charges defining the second line of the frame into voltage signals. Finally, the output terminals 17 and 18 supply the signals output by the detector 15 and those output by the detector 16 to the signal-processing circuit (not shown).
The two-line reading device shown in FIG. 2A has a color-filter array of the type shown in FIG. 4, wherein each column consists of two types of color filters, arranged alternately. This type of a color filter array will be referred to hereinafter, as "two-pixel periodic color filter array." As can be understood from FIG. 4, the two combinations of colors, i.e., two outputs 1 and 2 the terminals 17 and 18 generated during each even-numbered field period, are reversed during each odd-numbered field period. To prevent this reversion, it is therefore necessary to supply, as is shown in FIG. 5, the two outputs 1 and 2 of the solid-state imaging device 19 to the signal-processing circuit 22 through switches 20 and 21 which are controlled at the start of every field period. Since the detectors 15 and 16 most likely have different gains in most cases, an attenuator 23 is connected between the output 2 of the device 19 and the switch 21, thereby balancing the outputs 1 and 2 of the device 19.